Tube diffusers are conventionally used to support aerobic biological processes in wastewater treatment plants. A tube diffuser typically comprises a cylindrical flexible diffuser membrane that covers a rigid cylindrical support tube. Supplying pressurized air to the tube diffuser while the tube diffuser is immersed in wastewater has the effect of expanding the flexible diffuser membrane away from the support tube and causing the air to escape into the wastewater through a multiplicity of perforations in the flexible diffuser membrane. The effect is a plume of small bubbles that act both to oxygenate the biological processes occurring in the wastewater treatment tank and to provide a mixing function. Wastewater treatment in such a manner is described in, as just one example, F. L. Burton, Wastewater Engineering (McGraw-Hill College, 2002), which is hereby incorporated by reference herein.
Typically a flexible diffuser membrane is somewhat loose when applied to its underlying support tube. This looseness makes installation less difficult, improves the uniformity of the air distribution through the flexible diffuser membrane (particularly when air flow rates are low), and reduces the pressure drop associated with inflating and penetrating the diffuser membrane (i.e., head loss). However, this looseness also frequently negatively impacts the useful lifetime of a flexible diffuser membrane. A common failure mechanism for conventional flexible diffuser membranes is “flexure failures” or “destructive folding,” wherein buoyancy, wastewater velocity, and/or debris combine with the relatively loose fit of the flexible diffuser membrane to cause the flexible diffuser membrane to fold on itself (i.e., pinch) when the supply of pressurized air is turned off. With frequent on/off cycling of the pressurized air, as is common in, for example, Sequencing Batch Reactors (SBRs), this repeated folding ultimately causes the flexible diffuser membrane to tear.
For the foregoing reasons, there is a need for methods and apparatus that provide a solution for flexure failures in tube diffusers without negatively impacting ease of installation, gas distribution uniformity, and head loss.